In co-pending application Ser. No. 908,003, now U.S. Pat. No. 4,221,604 filed May 22, 1978, commonly assigned herewith, there is disclosed a method of forming mechanically strong hermetic seals by reacting antimony metal with glass frit. Glasses which were subdivided to form the frit of that invention were limited to those having softening points of less than 750.degree. C.
Most known sealing glasses foam (reboil) when heated in a vacuum to near their softening points. The problem faced by the inventor herein was developing a seal which was not only mechanically strong and hermetic, but which would remain stable, without foaming, when reheated in a vacuum to a temperature of at least 860.degree. C. The seal disclosed in copending U.S. application Ser. No. 908,003 now U.S. Pat. No. 4,221,604 cited above failed to meet the test of reheating in a vacuum to 800.degree. C.